Alex confirms a very important point that the 'west wall' of the Sphinx enclosure is unique at Giza, in his own words "unable to find any quarry face as weathered as the west wall of the enclosure." Bear this in mind.

Alex appears also to hold two other fundamental misunderstandings: 

1. When referring to Gauri's chemical weathering hypothesis, he cites the source of water as groundwater ("In this process, as salt-rich groundwater evaporates at the surface of the limestone, salt crystals precipitate between the particles"). Although in his earlier papers (1981) Gauri refers to 'subsurface' water, by the time of the conclusion of his studies (1995), because of the fact that similar chemical weathering was observed on freshly cut masonry (not in contact with groundwater) he firmly sees the source of moisture as dew condensing from humid air at nightfall ("The indicated mechanism of this exfoliation is that in the cool of night, with the arrival of the dew point, water vapour condenses on the stone surface"). Groundwater is not therefore a factor in Gauri's hypothesis.

2. Contrary to Alex's understanding, it is not only the western wall, however, that is heavily degraded, so too is the western end of the southern enclosure wall (up to the main fissure - of which more later). ("The problem with ScrySIE being the only process weathering the limestone is the difference between the west wall and the south wall of the enclosure. The west wall is clearly more weathered than the south wall").

So if you consider aspect as the cause of the unique degradation in the west of the Sphinx enclosure - you are faced with two major difficulties.

First, according to the TmW theory, the southern enclosure wall, which faces just east of north, should not be heavily degraded ("The south wall, through much of the year, gets blasted by this same radiation - but at a very oblique angle - the rock warms up more gradually, allowing relief of the stresses without fracturing"). And yet approximately 40% of the southern enclosure wall (the bit in the west) is heavily degraded. This is not consistent with TmW.

Secondly, the effects of all this serious infra red radiation as the sun breaks would be felt by ALL east facing exposures at Giza - of which there are scores. Some, in the central field cemetery, just sw of the Sphinx, are cut in the same limestone beds. It's not possible to be so certain about the stratigraphic correlation of other more distant exposures, such as the facade of the tomb of Debehen, but they are likely to be cut into similar, if not the same, units. But as Alex confirms, the degradation of the western Sphinx enclosure is not to be found elsewhere at Giza. Again the TmW theory is not consistent with the observable facts. Chris Ogilvie-Herald, kindly reminded me also that the chest of the Sphinx (no doubt that this is cut from the same limestone beds) faces east too - it does not show the same intensity of degradation as the western wall of the enclosure - TmW can't explain this.

Alex does not engage on two other important bits of evidence, which we discussed and which also tell against the TmW theory.

1. This theory does not explain how the Fourth Dynasty cutting (dated by Lehner and Hawass) in the Member I strata north of the Sphinx temple shows so little signs of degradation, yet the face into which this cutting is made is heavily degraded. Under any sensible interpretation this unweathered 4th dyn face has been cut into an older face.

2. There is evidence of water running in the Sphinx enclosure - again courtesy of Dr Lehner. There's a shallow drainage channel crossing the rocky floor of the Sphinx enclosure - issuing from the main fissure. This explains why the degradation of the southern enclosure reduces dramatically at this point. Water from up slope, encountered the main fissure and was directed into the enclosure and across the floor. So, as water-erosion has been present at some time in the area of the Sphinx, why should it not have affected the western enclosure walls?

Colin Reader

[Alex Bourdeau replied to this posting on the Amun list, his main point being that the interaction of weathering agents renders the analysis so complex that far more detailed measurement of the erosion surfaces at the Plateau is needed if proper conclusions are to be derived. I support this point of view entirely, but for what it is worth I feel that as the debate currently stands Colin somewhat has the edge - IL]